The present invention pertains to the general field of ophthalmologic surgical devices, and more specifically to the field of devices for performing corneal resectioning and methods therefor.
Numerous ophthalmic surgical procedures, such as for correcting myopia or hyperopia, require one or more steps of resectioning the cornea of the eye. A variety of devices called keratomes have been developed over recent decades to perform such corneal resectioning. Referring to FIGS. 1, 2a and 2b, a typical resectioning operation will separate flap 6 of corneal tissue 2 from eyeball 4. The tougher outer layers of epithelial cells 8 are separated and lifted away to expose the more compliant inner layers 12 of cornea 2, but the separated outer layers are left attached as flap 6. Once exposed, interior layers 12 of cornea 2 will to some extent adjust themselves, or their shape may be altered through further surgical steps. Such further steps may include, for example, making radial keratotomy cuts or performing a subsequent resectioning which may include removing a contoured layer of corneal tissue. At the conclusion of the various steps of the surgical procedure, flap 6 is typically replaced over inner corneal tissues 12 to protect the healing tissues.
The representative keratomes described in U.S. Pat. No. 5,496,339 issued to Koepnick, and U.S. Re. Pat. No. 35,421 issued to Ruiz et al., which are depicted in FIGS. 3a and 3b, demonstrate many standard features of prior art keratomes. A retaining ring for positioning and retaining the subject eyeball is typically supplied with a source of vacuum. The vacuum pressure draws the eyeball into the retaining ring so that the cornea protrudes through the retaining ring and presses against the surface of a feature, herein referred to as an applanation shoe, which is provided to restrain the protruding cornea. An applanation shoe has been found important in all known prior art.
However, an applanator impedes access to the eye under surgery. One approach to this problem is to make the applanator pivotable, or otherwise disengageable from contact with the eye, without a need to disengage the entire surgical apparatus from its positioning on the eye.
In order to resection the cornea, a cutting blade must be drawn through the corneal tissue, and both the thickness and the expanse of the corneal tissue which is cut must be carefully controlled. The separated portion of the cornea is typically left attached along one edge to form flap 6 which can easily be replaced over the cornea after the surgery.
Keratomes must have a mechanism by which the knife blade is guided. Proximate to the cutting location, the prior art keratomes all have blades rubbing on guides, or metal rubbing on metal, such as drive gears. Unfortunately, such rubbing can result in shavings being created and entering the surgical site. Referring to FIG. 3a, the keratome of Ruiz et al. has an intricate mechanism with metal-on-metal gears rubbing in the surgical vicinity. For example, pinion 834 rides on track 891 which is part of positioning ring 890; and endless pinion 822, along with its eccentric shaft and associated pinions, operates directly above the blade cutting site (not shown). In FIG. 3b, the keratome of Koepnick is seen to have blade 954 which rubs directly on the insert 948 and slides in surfaces defined along line 991. The sliding surfaces at 991 are located directly above positioning suction ring 990, and the rubbing surface between blade 954 and insert 948 is directly adjacent regions of intimate contact between the corneal tissue and insert 948. Thus, these two prior art keratome examples have rubbing between the cutting blade and other surfaces, and rubbing of gears, very close to the surgical site.
Another drawback of existing keratomes is the inconvenience of maintaining surgical cleanliness. Since parts of the keratome must be in intimate contact with tissues around and including the surgical site, it is necessary to ensure a high degree of cleanliness and sterility. The relatively intricate mechanisms which prior art keratomes position near the surgical site, as described above, have not been well-adapted for ease of cleaning and autoclaving.
Thus, a need exists for an easily used keratome able to perform precise resectioning operations, while facilitating surgical cleanliness by avoiding creation of shavings which might contaminate the surgical site, and by being easily cleaned, sterilized, and replaced.
A keratome in accordance with the present invention enables an ophthalmologic surgeon to perform corneal resectioning, separating a flap of corneal tissue for later replacement, without a need for an applanator, and without any rubbing of parts of the surgical device near the surgical site.
In accordance with the present invention, the surgical device preferably includes a surgical unit having cutting head elements mounted on a drive assembly, and also includes a control unit and a foot pedal. During surgery, the cutting head elements are in intimate contact with the subject eye, for positioning and cutting. The drive assembly element supports and drives the cutting head elements. The control unit is the preferred source of power and vacuum for the surgical unit, and it supplies power and vacuum according to settings entered by the user. The foot pedal allows the user to give commands to the surgical device without requiring use of hands. The surgical unit is preferably hand-held and easily positioned over the subject eye.
The preferred surgical unit includes three distinct elements. Two of these are xe2x80x9ccutting headxe2x80x9d elements which must contact the eye during corneal surgeryxe2x80x94a positioning ring assembly and a blade fork assembly. These two cutting head elements extend from the third element, a drive assembly, in such a way that interference and rubbing between the cutting head elements proximal to the surgical site is minimal or entirely absent. Preferably, the two cutting head elements are easily removed and as easily replaced onto the third element, the drive assembly, without a need for tools, so the surgeon can ensure sterility by simply attaching fresh and sterile replacements for the cutting head elements.
In a preferred embodiment of the present invention, a blade fork assembly suspends a cutting blade between the positioning ring and the applanation shoe and guides the cutting blade near to the applanation shoe. The thickness of the cut is preferably controlled by a guide, which is disposed a controlled distance away from the cutting blade. The outer layer of corneal tissue is separated by the blade as it passes between the blade and the guide, so that the thickness of the separated layer is controlled by the spacing between the blade and the guide.
The blade fork assembly is caused to move by the drive assembly, which imparts two distinct movements to the blade fork assembly during cutting action. One movement is a high-speed lateral oscillation, and the other, imparted at the same time, is a slow smooth forward movement. The drive arm impel the blade fork forward as long as it is commanded to do so through the control unit, until the drive arm impinges on an adjustable stop mechanism, thereby causing a clutch to slip and preventing further forward displacement of the drive arm.
The blade assembly is preferably entirely suspended and does not touch any part of the mechanism which is near to the surgical site except indirectly by way of the blade fork drive arm which supports the blade assembly.